Octave range too small, notes too high

[einsteinx2]

Hi everyone, and thanks in advance for any help. I've had an original Adafruit x0x kit sitting around for a couple years and finally got around to building it this last week. Everything seems to be working fine with the sequencer and the synth itself seems to be working as it should with all knobs doing their intended function. The only issue I'm having is with tuning.

The lowest I've been able to get the low C to go with TM5, TM4, and the tuning knob all the way down is about 74 Hz (checking with a multimeter with frequency function). When I put things around center, that lowest C is at around 130 Hz. Also the octave spread between two Cs is only about half of the lower C's frequency, though it gets wider as I get higher up the scale (but still not double).

I'm not really sure where to start looking for a problem. I'm guessing this is a VCO issue, but could some other section be affecting the VCO output? I was very thorough during the build, verifying every resistor with the multimeter before using it and double checking everything, though of course it could be some other faulty component or I simply made a mistake without realizing it.

Any suggestions on what to verify?

[guest]

check the cv out
and see if its linear with notes
it should increase 1v/octave
with the lowest c being 1v

[einsteinx2]

check the cv out
and see if its linear with notes
it should increase 1v/octave
with the lowest c being 1v

Thanks for the reply. Voltages at CV seem to be correct. Starting with the lowest C going up each octave using keyboard mode I'm reading 1.027, 2.028, 3.005, 4.00, and the steps in between seem to be relatively even. My voltages on J4 are fine (5.33 on pin 1 and 12.00 on pin 3) so it's not an issue there either.

I'm starting to wonder if my multi-meter is reading things wrong in frequency mode. It's been giving me some inconsistant readings (like starting up at a few hundred then slowly falling down, maybe because it does RMS?)... But just by ear the lowest note sounds too high.

Am I correct in measuring pin2 of the waveform switch to check the Hz? Is there any additional place I can check? I'm going to download a guitar tuner VST and see if I can get an accurate reading off of the x0x output.

[einsteinx2]

Just used a guitar tuner VST and I'm getting 216 Hz hitting the lowest C button with TM3, 4, 5, and the tuning pot at about center.

[einsteinx2]

Also, it seems like the slide function is not working. Or it works in the sense that I can enable it, but the sound fades out rather than staying steady. Unless I'm misunderstanding the function of that button...

In pattern mode, when I enable the 'S' key on a note, it should sustain at full volume right? Right now if I string together say 8 C notes, only the first one hits then the sound fades out by the 2nd or 3rd note.

I'm going over the board now to see if anything looks out of place. I swear the notes were lower by at least an octave last night, while today they are much higher (over 200Hz on bottom C). I'm guessing some loose component got knocked when I was re-seating the board. I socketed a couple dozen components, not counting the ICs so that it would be easier to do mods later. Possibly one of them is loose or something. Though most of the chips I socketed were after the VCO, and it seems to be a VCO issue since the voltages are correct but the note at the VCO is much too high.

[einsteinx2]

I started going through the VCO section of the manual and testing with the 3V C playing over and over.

Looks like I'm getting some incorrect values. Specifically, R90, which should be reading that same 3V, is reading 5.33 volts (unless I'm misunderstanding that measurement), though pin 7 of the op-amp is reading the correctly at 3V.

Also, the DC bias for my saw wave is reading 10.33, not 8.5 (this check here: http://www.ladyada.net/images/x0xb0x/fa ... eter_t.jpg)

Some things are testing correctly though. The tests higher up on that page in the manual (5.33V and 12V tests at the diode and IC) are testing perfectly. Just for whatever reason the VCO is generating very high frequencies. My 3V C is generating 535 Hz on the waveform switch (edit: I've had it on running C notes since this post, and now it's measuring 430Hz, quote possibly something wacky with the multimeter, but it's definitely way higher than it should be just by ear).

Am I testing the correct place on that switch? I have the switch on saw, and am testing this pin:
OOOXO
O____O

[guest]

your cv is definitely off
it should be 1.00v 2.00v and 3.00v for all the c's
a few millivolts makes a big difference audibly

actually its fine if its not exactly x.00v
but rather that c1 - c2 = c2 - c3 and so on
and this needs to be accruate to a few millivolts

ive never trusted the hz measurements on multimeters

here is what the output should be
1v = 32.7hz
2v = 65.4hz
3v = 130.8hz
4v = 261.6hz
5v = 523.2hz

yours sounds way off and drifting
which might be a bad solder joint
or a bad ptc thermistor

turn off the power
and double check the resistance of r100 r106 and tm5

slide only ties notes together
it does not sustain them forever
so its probably working fine

[guest]

also
check out this post
viewtopic.php?f=12&t=24759

[antto]

the multimeter could be failing to detect the frequency, since the x0x has a bit irregular waveforms
maybe record a sample of 4 C notes on the different octaves so we can hear..
did you double check if the trimmers and resistors around the VCO (and pitch CV specifically) are the correct values?

[einsteinx2]

I just went through the whole VCO section in the build manual and verified all the resistors. Also verified that TM4 and TM5 are correct as per the manual. Also, looked over that whole section on both sides, all the solder joints look good, no obvious mistakes or joints touching.

The really weird thing is that when I first tested my x0x, the keys were lower by a couple octaves. Still too high, but not nearly as much as now. Then the next morning everything had jumped forward a few hundred Hz. It's stayed the same since then. Does that give any clues to what component it could be?

I saw that other thread with the tuner VST and have it set up and everything, but the lowest I can tune is many octaves above where it should be, so I can't get much use out of that yet.

Really bummed about this. If this were code, I'd have no problem, but I'm not experienced with hardware debugging.

I found a diagram on the forums with voltage levels for all the components. I guess I need to just sit down, loop a C, and check all the voltages to see where things start going off.

In any case, since the Hz at the waveform switch is so much higher than it should be, does that point to it definitely being a problem with the VCO?

I'll post up a quick recording soon so you can hear.

[guest]

the problem is either the vco or the dac
can you post up
all the voltages on ic9 and ic11
for c2 and c3